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Subject: RE: [plcs-dex] RE: [plcs] Classification of SI Units
Dear Tom,
Thanks for your view. On the whole this is the way that I see things. However, when I raised this is one PLCS session at Fort Lauderdale, there were voices suggesting that the RDL would handle all cases. I suppose that derivation and conversion are possible through the reference data (somehow) but I am leery of breaking compatibility with other STEP APs. We are in the territory as to whether the reference data should only extend the AP or whether replacing valid STEP constructs is permissible.
I am not entirely sure what you mean when you say "to base everything on SI". I am wondering whether this is possible with all the forms of units of measure. What comes to mind are things like "can" and "reel". Perhaps you mean these should be conversion based units and "can" should be converted to "5 litres" for instance (cans of paint) and reel to "10 metres" (reels of wire)? The only problem that comes to mind is that the paint cans might be 5 litres but the oil cans 10 litres.
Cheers,
Tim.
-----Original Message-----
From: Hendrix, Thomas E [mailto:thomas.e.hendrix@boeing.com]
Sent: 30 July 2004 22:17
To: Tim King; ian.bailey@eurostep.com; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: RE: [plcs-dex] RE: [plcs] Classification of SI Units
If we classify as-is, Conversion_based_unit and Derived_unit are never used, each unique unit value generates a separate external class in a one-level system, with no semantic relationships among the classes. Does this adds much?
Or maybe can we create some analog of the derivation and conversion structure as (static) class structure? I am not seeing a nice way to do this.
So I prefer to build derived units and conversion based units explicitly where applicable. Further it seems reasonable to me to base everything on SI. That is the 203 recommended practise.
-----Original Message-----
From: Tim King [mailto:tmk@lsc.co.uk]
Sent: Thursday, July 29, 2004 1:20 AM
To: 'ian.bailey@eurostep.com'; plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: [plcs-dex] RE: [plcs] Classification of SI Units
I think the problem has another related aspect. Use of classification can also cover another key feature within the modules for units, namely derived units. If one has the unit "m/s^2" does one classify as is or does one use the drived unit feature to build the unit from the constituent units? My preference would be to build the derived unit because this supports full dimensional analysis for validation of calculations. However, for those who do not see the benefit of this capability, quite clearly classification offers an attractive "short cut" that circumvents the complexity that is necessary to represent the full derivation. If we end up with a "mixed economy" then we will not be able fully to harmonise and compare data sets.
Cheers,
Tim.
-----Original Message-----
From: Ian Bailey [mailto:ian.bailey@eurostep.com]
Sent: 28 July 2004 21:55
To: plcs@lists.oasis-open.org; plcs-dex@lists.oasis-open.org
Subject: [plcs] Classification of SI Units
Hi Folks,
I've been working on the "representing_properties_numerically" capability, where an issue has been raised by Tom Hendrix. We have been classifying (i.e reference data) the units which are used with properties. Tom has pointed out that the STEP models have a full breakdown of SI units already and there could be a conflict between the value set there and what is classified. Has anyone looked into this issue ?
Regards
--
Ian Bailey
Eurostep Limited - www.eurostep.com
t&f: +44 (0) 20 7378 1894
m: +44 (0) 7768 892362
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